In a typical storage battery, such as a lead-acid battery, electrode grids are suspended in an acid contained within a cell having plastic walls. Each of the positive electrode grids typically is composed of a metallic lead or lead alloy grid structure composed of metallic grid members. A chemically active material is located within, and is held by, each positive electrode grid. This material is typically a chemically active paste. The cross section of the grid members is typically hexagonal, in order to hold the paste firmly in place.
A major cause of premature failure of storage battery cells, particularly lead-acid cells, involves growth of the electrode grids in such cells, particularly the grids of positive polarity. This growth typically is caused, at least in part, by the formation of lead oxides on the positive grid. In turn, the spacings (distances) between the positive grid members tend to increase in all directions, whereby the grid tends to expand or grow away from all sides of active material or paste located within the grid structure. At the same time, the active material or paste does not remain sufficiently flexible to adjust to the changes in spacings. Hence, the grid members pull away from, and loses physical contact with, the active paste material. Consequently, a significant drop in the retrievable electrical storage capacity of the pasted grid prematurely results, whereby a significant decrease in the useful lifetime of the battery results. The loss of physical contact can also increase to such an extent that some of the paste drops from the grid and falls to the bottom of the cell, whereby other problems can arise, such as electrical shorting of positive to negative electrodes, whereby battery lifetime likewise is undesirably decreased.
In U.S. Pat. No. 3,556,853, issued to me on Jan. 19, 1971, entitled "Grid for Lead-Acid Cell," a positive electrode grid structure was disclosed which alleviated the foregoing problem. The structure involved a plurality of metallic grid (structural) members each having a closed geometric shape (contour)--for example, a plurality of concentric rings--each (except for the outermost) being enclosed within another--joined together by interconnecting metallic support members, to form a unitary (one-piece) electrode structure. These structural members were dimensioned such that the ratio of the (outer) surface area to the cross-section area--i.e., the "growth ratio"--for any specified structural member was no greater than such ratio for all structural members contained within the specified member. The (outer) surface area of a structural member was defined as the product of circumference and perimeter. Although such a grid structure, satisfying such a growth ratio relationship, yielded significant improvements in useful battery lifetime, it imposed an undesirably low upper limit upon the overall size and hence electrical capacity of the cell for a given diameter thereof. This low upper limit arose because, for a given innermost structural member, the outermost structural member had to be made so thick that not enough (if any) space between structural members remained for sufficient (if any) paste. Conversely, for a given outermost structural member, the innermost structural members had to be made too thin to be practical.
It would therefore be desirable to have a new design for grid electrode structure which alleviates the foregoing problem.